The induction of hemoglobin production in Friend leukemia cell lines stimulated by DMSO also may be stimulated by various drugs or combinations of drugs that interfere with protein, RNA or DNA synthesis. At the onset of differentiation there is no decrease in viral 60-70S RNA production, but the released particles exhibit reduced reverse transcriptase activity. The DNA polymerase of Herpesvirus saimiri has been purified by DEAE- and phosphocellulose chromatography and the salt, pH, temperature and template optima have been determined.